A centrifugal fan is known as an air blower and is widely used for cooling, ventilating, and air-conditioning in household electrical appliances, office equipment and industrial equipment, or air-conditioning and forcing air in an automobile, etc. As a conventional centrifugal fan, a centrifugal fan in which a casing is formed by an upper casing and a lower casing, and an impeller is housed between the upper casing and the lower casing, and air drawn in from a suction port by rotating the impeller is discharged outwardly from a blowing port formed on a side surface between the upper casing and the lower casing, is known (see Japanese Unexamined Patent Application Publication No. 2012-207600).
FIG. 7 shows a centrifugal fan 100 described in Japanese Unexamined Patent Application Publication No. 2012-207600. In the centrifugal fan 100, a squared shaped casing 120 is formed by an upper casing 121 and a lower casing 122, and an impeller 130 is housed between the upper casing 121 and the lower casing 122. The impeller 130 has a circular shroud 131. The air drawn in from a suction port 110 by high-speed rotation of the impeller 130 is passed through blades 135, it is blown outwardly from an out periphery of the impeller 130, and it is discharged outwardly from a blowing port 111 formed on a side surface between the upper casing 121 and the lower casing 122.
In Japanese Unexamined Patent Application Publication No. 2012-207600, a specific structure in the case in which the centrifugal fan is installed in a housing of another device or apparatus is not described. The centrifugal fan described in this document is fixed to a housing of a device or apparatus generally by forming flanges which extend outwardly in a radial direction at multiple positions, and by passing bolts, screws, etc., through pass-through holes formed at the flanges.
However, in the case in which high accuracy of positioning of the centrifugal fan is desired, the centrifugal fan cannot be easily positioned and high accuracy of the positioning cannot be easily performed, even if it is fixed to the housing of the device or the apparatus by using the bolts, screws, etc., as described above. Furthermore, in the centrifugal fan having a conventional structure described in Japanese Unexamined Patent Application Publication No. 2012-207600, it is necessary that the centrifugal fan be made thin by decreasing total height thereof, when a mounting space for the centrifugal fan is small. In this case, since it is also necessary to use a thin type impeller, a cross-sectional area of a passage at an air suction side of the impeller is decreased, and ventilation resistance is increased, and as a result, noise is increased.
In view of such circumstances, an object of the present invention is to provide a centrifugal fan that can be easily positioned when installed in a device or apparatus, which can further improve positioning accuracy, and which can decrease noise, even if it is made thin.